Digital technology has become pervasive in the creation and distribution of many types of media. For example, valuable audio and video content is distributed in digital form both electronically and embodied in a carrier media. Similarly, documents may be created and distributed in digital form both electronically and embodied in a carrier media such printed paper. Content owners may wish to provide identification, authentication and non-repudiation for certain documents transmitted in electronic form. Furthermore, many valuable documents are produced and distributed in paper form. Various technologies are now readily available for making high-quality copies of documents. As a result, unauthorized copying and counterfeiting of documents such as bank notes, checks, and identification documents is a serious concern.
Moreover, the pervasive nature of the Internet allows easier and anonymous access to sources of counterfeit documents. There are many image capture systems such as CCD cameras, drum scanners, flatbed scanners and other capture/scanning systems that are readily available and that provide excellent reproduction accuracy and precision. Similarly, general-purpose personal computers have the capacity to run powerful digital media editing software that is also readily available. Furthermore, very accurate and precise monochrome and color printing systems are readily available for outputting such unauthorized copies and counterfeit documents. Several technologies are available to thwart the unauthorized copying or counterfeiting of documents including UV ink, holograms, and OVDs (Optical Variable Devices). Such techniques may be relatively inexpensive, but may rely on human operator judgment and may not be reliable. Documents may also be tagged using RFID or DNA tagging technologies. Such techniques may be reliable, but may be relatively expensive.
Several types of physical document copy detection systems are known including copy detection patterns (CDPs) that may be placed in a particular region of a document reserved for the purpose. Furthermore, several copy detection systems are known that utilize visible and invisible digital watermarks that are applied to an actual image or document. Commercially available systems include those available from Digimarc Corporation of Beaverton, Oreg. and Mediasec Technologies, LLC of Providence, R.I. For example, a system for using a continuously varying tone graphic field for copy detection is described in U.S. Pat. No. 6,454,174 entitled Method for Reading Electronic Tickets, issued Sep. 24, 2002 to Ronald P. Sansone. Furthermore, U.S. Pat. No. 6,782,116 B1 issued Aug. 24, 2004 to Jian Zhao, et al. describes watermark systems and is titled Apparatus and Methods for Improving Detection of Watermarks in Content that has Undergone a Lossy Transformation.
However, traditional copy detection patterns may not be effective across a variety of paper types. Accordingly, there is a need for a copy detection pattern based copy detection system that provides robust copy detection across multiple paper types. Accordingly, there are several disadvantages of currently available systems and methods for detecting counterfeit documents using copy detection patterns.